Inflatable packers or bridge plugs have long been used in wellbore operations. An inflatable packer typically comprises a tubular base and a surrounding, inflatable elastomeric bladder or sleeve. Fluid passages within the tubular body allow fluids to contact the inflatable bladder and expand the bladder radially outwardly to effect sealing engagement with a borehole or well casing.
Since the elastomeric bladder is subjected to both expansion pressure and abrasion or cutting forces, it has been common to surround the exterior surface of the bladder with a plurality of peripherally overlapping, resilient reinforcing slats or ribs. There is generally sufficient overlap of such slats that upon expansion of the inflatable bladder, the slats remain as a surrounding armor protecting the bladder from abrasion and cuts while also preventing extrusion of the bladder elastomer between the slats in a localized area. The slats are commonly welded to a portion of the assembly to retain their desired position and orientation. U.S. Pat. No. 5,143,154 describes one form of slat weldment.
Because the slats cannot effect the sealing of the packer against a wellbore or casing, at least some portions of the reinforcing slats are surrounded by and may be bonded to an outer annular elastomeric cover or packing element which, upon expansion of the inflatable packer, comes into pressure sealing engagement with the wellbore or casing.
The outer sealing cover generally comprises either a single or a plurality of annular circumferential elastomeric pieces located on the outer surface of the reinforcing slats. When a single elastomeric piece is employed it may cover only a portion of the longitudinal length of the slats or, alternatively, it may cover the entire outer surface of the slats. Such single piece covers generally have a uniform thickness along their length, the thickness generally being substantial. Such arrangements are described in U.S. Pat. Nos. 3,837,947, 4,832,120 and 5,143,154.
Slat reinforced inflatable packers are typically constructed of high strength, cold-worked slats welded to an end connector. The resulting heat affected zone of the slats has significantly lower strength (as much as 70% lower strength) than the unwelded portions of the slats. Such a condition substantially reduces the overall strength of the packer.
In the assembly of a slat-reinforced inflatable packer, the welded end portions of the slats are surrounded by a high strength metal sleeve. The sleeve, in addition to its function of protecting the welded end portions of the slats, acts as a mandrel around which the slats are bent upon inflation expansion of the inflatable packer.
In the aforementioned U.S. Pat. No. 5,143,154, the assembly of the packer requires the placement of the high strength metal surrounding sleeve along the slats prior to slat weldment. The sleeve can then be slid longitudinally outwardly along the slats to cover the end portions and to engage the retaining shoulder provided on the collar to which the slats are welded. No heat treatment of the welded slats to restore the strength lost in the heat of the welding operation is possible without a consequent loss in the desired high strength properties of the surrounding sleeves. The sleeves must be an integral part of the assembly prior to welding.